1. Field of the Invention
The field of the invention is in general terms, that of motor vehicle headlights.
2. Description of the Related Art
In this field, various types of light or lighting devices are known, among which there are:                side lights, with low intensity and range;        high beam lights, and auxiliary lights of the long range type, where the area of vision on the road is around 200 meters, and which must be switched off when passing another vehicle in order not to dazzle its driver; these are beams without cutoff;        improved headlights, referred to as dual function, which combine the functions of dipped lights and high-beam lights by incorporating a removable screen;        fog lights;        and, more particularly relating to the invention, low beams or dipped lights, of high intensity and a range on the road of around 70 meters, which are used essentially at night and where the distribution of the light beam, with generally a V-shaped cutoff, is such that it makes it possible not to dazzle the driver of a vehicle being passed.        
FIG. 1 depicts schematically a projection 101 onto a vertical plane of the light being produced by a lighting device of the low beam type. The flat projection surface is disposed facing the lighting device in question, perpendicular to its optical axis. The hatched part of the projection corresponds to an absence of light in this part, the part left white corresponding to a normal illumination by means of the lighting device in question.
The projection 101 has a non-flat cutoff line 105, essentially consisting of a low horizontal part 110, followed by a step 111, consisting of an oblique segment at the projection of the optical axis, and then a high horizontal part 112. Such a configuration make it possible not to dazzle the drivers being passed, to the left in the example in question, whilst providing optimum lighting on the right of the road.
In general terms, a cutoff line is a limit illumination line above which illuminating the road is prohibited. In countries with right hand traffic, this cutoff line is horizontal over the entire width of the road and on the left-hand verge of the road; it forms for example an angle of 15° above the horizontal, on the right-hand verge of the road. Its role is to prevent the vehicle lighting dazzling a driver in a vehicle in the opposite direction or the vehicle preceding it. The remainder of the document is illustrated by means of examples applicable to right hand traffic. The various examples described are of course directly transposable to conditions with left hand traffic.
There exist two main families of optical modules, which correspond to two distinct arrangements of the optical modules and which are able to participate in the lighting device according to the invention. Optical module means an optical system comprising at least one light source, for example one or more light emitting diodes grouped together, or a halogen or xenon lamp, possibly disposed in a reflector, and which is preferably “autonomous”, that is to say which is able to be switched on or off separately from the other optical modules of the lighting device in which it is installed.
The two main families of optical module are as follows:
The first family is that of so-called elliptical optical modules. In this type of light, a light concentration spot is generated by a light source disposed in a mirror. Typically, the light source is disposed at the first focus of an ellipsoidal shaped mirror, the spot forming at the second focus of the mirror. The light concentration spot is then projected onto the road by a convergent lens, for example a lens of the plano-convex type.
The second family is that of so-called reflection optical modules with a complex surface or a parabolic surface. In this type of optical module, a light beam is generated by a light source of small size disposed in a reflector, or mirror. The projection onto the road of the light rays reflected by a suitable reflector makes it possible to directly obtain a light beam complying with the various constraints imposed by standards. This family of optical module includes so-called free-surface, or complex-surface, lights, that make it possible to directly obtain a light beam having a required cutoff line.
As specified subsequently, the lighting device according to the invention involves optical modules that may belong equally well to the first family or to the second family.
The conventional lighting devices that have just been mentioned, more particularly those that are used as dipped lights, produce light beams that are open to improvement when they are used under certain conditions. Thus, for example, when a vehicle is entering a bend, the headlights continue to illuminate straight in front of them whereas it would be more judicious to orient the light beams in the direction of the bend being taken. This is why, in addition to the conventional main headlight functions, in particular dipped and main beam, various improvements have gradually appeared.
Thus elaborate functions have been seen, referred to as advanced functions, or AFS (“Advanced Front Lighting System” in English, meaning advanced front lighting system), among which there are in particular a so-called “Town Light” in English, meaning town light, which provides the broadening of a beam of the dipped type while slightly reducing its range; a so-called “Motorway Light” function in English, meaning motorway light, which provides an increase in the range of a dipped light; a so-called AWL (“Adverse Weather Light” in English, meaning adverse weather light), which provides a modification of a dipped light beam for preventing any dazzling through a reflection of its own headlight.
In functions of the AFS type, there are also found, directly relating to the invention, a so called DBL function (“Dynamic Bending Light” in English, meaning movable bending light, called code virage in French), which produces an orientable headlight, also referred to as a movable beam lighting device: such a lighting device is able to modify the orientation of a light beam produced by a lighting device, so that, when the vehicle is entering a bend, the road is illuminated in an optimum fashion, following the geometry of the road.
In order to fulfill such a function, a first known technique consists of making the global beam of the lighting device movable by virtue of an actuator controlling the pivoting of the lighting device in its entirety according to information coming from the vehicle, for example by means of a steering-wheel angle sensor. An articulated lighting device is then spoken of. An example of implementation of this first technique is described in the patent FR 2 846 609, which is equivalent to U.S. Pat. No. 7,280,901.
A second technique, such as the one described in the patent application FR 2 857 921, which is equivalent to U.S. Patent Publication 2005/0018436, consists of a fixed light projecting device comprising a plurality of light sources, and means for controlling a successive switching on of supplementary light sources, the successive switching on of the sources depending on the path of the vehicle so as to provide an effect of light sweep towards the inside of the bend being entered.
The second technique is today essentially used with light emitting diodes. This is because such light sources are more and more being used in lighting devices, which take advantage of several properties of light emitting diodes:                first of all, for a long time, it has been know that light emitting diodes do not radiate omnidirectionally but radiate in a half-space opposite to the substrate that supports its p-n junction; thus, by using a more directive radiation than halogen or discharge lamps, the quantity of energy lost is less. The diodes consume less energy, even at equal intensity of radiation, than discharge lamps or halogen lamps.        next, these diodes were recently improved in terms of radiation intensity; they can now radiate a flux of at least 100 lumens. The quantity of heat that they give off is however limited, and a certain number of constraints, relating to the dissipation of heat in the lighting devices using other types of light source, disappear.        in addition, they emit radiation, for a long time in the red range but now also in white; in addition, they are compact, and their particular shape offers novel possibilities for producing and arranging the complex surfaces that are associated with them. They make it possible to work the style of the lighting devices by facilitating the creation of original shapes.        
However, in the second technique mentioned for fulfilling DBL functions, in particular by using light emitting diodes as supplementary light sources, the size of such a lighting device is very great, in particular because of the number of LEDs that are added as supplementary light sources; in addition, such an addition makes this solution particularly expensive.
Moreover, in the first technique mentioned, because of the relatively low light intensity that the LEDs are capable of producing, it is necessary to arrange a large number of them within the lighting device. Making all the LEDs move in such a lighting device is then complicated in two ways: firstly, the bulk due to the movement mechanism and of the diodes themselves is maximum, and secondly the weight of the elements to be moved in order to make the light beam pivot is significant and gives rise to high play between the various elements involved in the movement.